Add a note that generated files are generated.

Folks keep assuming checked-in assembly files are the source. Between
the preprocessor, delocate, NASM not using the C preprocessor, and GAS's
arch-specific comment syntax, comment markers are kind of a disaster.
This set appears to work for now.

Change-Id: I48e26dafb444dfa310df80dcce87ac291fde8037
Reviewed-on: https://boringssl-review.googlesource.com/c/33304
Commit-Queue: Adam Langley <agl@google.com>
Reviewed-by: Adam Langley <agl@google.com>

crypto/perlasm/arm-xlate.pl

@@ -141,6 +141,9 @@ sub expand_line {
 }
 
 print <<___;
+// This file is generated from a similarly-named Perl script in the BoringSSL
+// source tree. Do not edit by hand.
+
 #if defined(__has_feature)
 #if __has_feature(memory_sanitizer) && !defined(OPENSSL_NO_ASM)
 #define OPENSSL_NO_ASM

crypto/perlasm/ppc-xlate.pl

@@ -256,6 +256,9 @@ my $darn = sub {
 };
 
 print <<___;
+# This file is generated from a similarly-named Perl script in the BoringSSL
+# source tree. Do not edit by hand.
+
 #if defined(__has_feature)
 #if __has_feature(memory_sanitizer) && !defined(OPENSSL_NO_ASM)
 #define OPENSSL_NO_ASM

crypto/perlasm/x86_64-xlate.pl

@@ -1123,6 +1123,16 @@ my $endbranch = sub {
 
 ########################################################################
 
+{
+  my $comment = "#";
+  $comment = ";" if ($masm || $nasm);
+  print <<___;
+$comment This file is generated from a similarly-named Perl script in the BoringSSL
+$comment source tree. Do not edit by hand.
+
+___
+}
+
 if ($nasm) {
     print <<___;
 default	rel

crypto/perlasm/x86asm.pl

@@ -255,9 +255,16 @@ sub ::asciz
 
 sub ::asm_finish
 {   &file_end();
-    print "#if defined(__i386__)\n" unless $win32;
+    my $comment = "#";
+    $comment = ";" if ($win32 || $netware);
+    print <<___;
+$comment This file is generated from a similarly-named Perl script in the BoringSSL
+$comment source tree. Do not edit by hand.
+
+___
+    print "#if defined(__i386__)\n" unless ($win32 || $netware);
     print @out;
-    print "#endif\n" unless $win32;
+    print "#endif\n" unless ($win32 || $netware);
 }
 
 sub ::asm_init